We need some clarification.
What is the exact rule? Is this a business rule? Or referential constraint?
IsPrimaryFlag appears to be an attribute of the Address entity.
We use our human intelligence to put it into immediately the data integrity context.
Russel...what if the non-primary address entered first into the system? How the first design any different than the second?
Without knowing more about it, trigger or application enforcement would both be appropriate.
Kalman Toth - Database, Data Warehouse & Business Intelligence Architect
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